In a semiconductor device manufacturing field, to form desired patterns on a substrate such as a semiconductor wafer by applying a film deposition process and an etching process has been conventionally in practice. When a STI (Shallow Trench Isolation) process is carried out in such a semiconductor device manufacturing step, a deposit of a silicon oxide (for example, SiO2 or SiOBr) is deposited on sidewall portions of the patterns. Conventionally, the removal of such a deposit has been performed by, for example, a process using single gas of hydrogen fluoride (HF).
However, when the composition and the bonding state of the deposit are close to those of silicon dioxide (for example, gate oxide films) being structures in the patterns, there is a problem that a selection ratio to these cannot be taken. Incidentally, water being a bi-product generated by a reaction between the deposit and hydrogen fluoride (SiO2+4HF→SiF4+2H2O) accelerates the reaction to cause a chain reaction, so that not only the deposit but also the silicon dioxide being the structures in the patterns is sometimes scraped away. Further, when the queuing time (q-time) after the etching process is long, the selection ratio sometimes becomes worse due to an influence of the water depending on a moisture absorption state of the deposit.
As an art to remove a natural oxide film formed on a surface of a silicon substrate, there has been known an art to use hydrogen fluoride vapor and H2O or alcohol vapor. However, this art is an art to remove the natural oxide film and is not an art to remove a deposit deposited on sidewall portions of patterns.
There has also been disclosed an art to continuously etch a polysilicon film under an etching condition having high etching selectivity after removing a natural oxide film formed on a surface of the polysilicon film by exposing the polysilicon film to hydrogen fluoride gas in a vacuum region. When the oxide film is etched by using etching gas containing carbon, an etching by-product containing a carbon-based substance adheres on the surface of the polysilicon film.
As described above, when the deposit deposited on the patterns is removed, there has conventionally been the problem that selectivity between the deposit and the silicon dioxide being the structure in the patterns is low, so that the silicon dioxide being the structure in the patterns is damaged. Further, there has been the problem, that, when the queuing time (q-time) after the etching process is long, the selection ratio further worsens due to the influence of water depending on the moisture absorption state of the deposit.
Further, detailed studies by the present inventors have led to the findings that using gas containing carbon as etching gas when silicon and film species before/after it are etched causes a problem that a deposit sometimes contains organic matter, and in this case, the method of removing the deposit of silicon oxide (for example, SiO2 or SiOBr) cannot completely remove the deposit.